Thermionic modulator



Feb. 16 1926. 1,573,282

J. S. STONE THERMIONIG MODULATOR Filed Nov. 23, 1923 f7 5 il? WA TroRNEv' Patented Feb. 16, 1926.

UNITED 'STATES PATENT OPT-funs.

JOHN STONE STONE, F SAN DIEGO, CALIFORNIA, ASSIGNOR TO TELE- PHONE AND TELEGBAPH COMPANY, A CORPORATION 0F NEW YORK.

THEBHIONIC IODULATOR.

Application med November 23, 1983. lerial No. 876,625.

To all whom it may concem:

Be it known that I, JOHN STONE S'roNn,

residing at San'Diego, in the county of San Diego and State of California, have invented certain Improvements in Thermionic Modulators, o f which the following is `a speciiication.

An object of my invention is to provide a new `and improved device and method for modulation of an alternating current for signaling and other purposes. .Another object of my invention is to provide a system in which the modulating force is ap lied most effectively. Still another object is to provide athree-electrode thermionic tube modulator with means for applying the modulating force in an eliicient manner. These and other objects of my invention will become apparent on consideration of a limited number of specific examples of the invention, which are disclosed 1n vthe following specitication and which I now roceed to descrita with the understanding t at the invention is defined in the appended claims. Referring to the drawings, Figure 1 is an elementary diagram illustratin the principle involved in my invention, igs. 2 and 3 are diagrams showing simple modiications, Fig. 4 is'a diagram showin anotherlicaton of the invention and ig. 5 is 'agram to which reference will be made in explaining one of the advantages of the invention.

Referring to Fig. 1, this shows a threeelectrode thermionic vacuum tube with simple associated circuits. In accordance with the usua. recognized theory, its operation is known to be in conformity with the following equation:

where Ip is the plate circuit current, stands From Fig. 1, it is at once apparent that- Elz'Ec-I-e--rIp (2) Substituting -rom equations (2) and (3) in equation (1) the result is obtained that- Ip=f[%2+E,-|e r-xfn] (4) From this it is evident that the resistance r in the common branch of the grid and plate circuits is equivalent to a resistance (LI-0r in the plate circuit, so far as it af? fects the plate current. That is, the resistance 1' placed in the common branch is more effective to alter the plate current than it would be if introduced inl the plate circuit alone. A very simple modulation system canl be made to utilize this roperty, as shown, for example, in Fig. 3, where a microphone transmitter is introduced in the common branch of the plate and id circuits. Its variation of reslstance un er the inllu- 'ence' of voice waves will be more effective in varying the output plate current than if the microphone were introduced in the plate circuit alone. In Figs. 2 and 4 the same principle is involved in a simple elementary radio transmitter.

Instead of introducing the telephone transmitter directly between the points marked 1 and 2 inFig. 2, I have there shown the transmitter included in a resistance amplifying loop (j, L3 and the transmitter is shunted by a distortion reducing resistance coil R. In this case, if the resistance of the transmitter is amplified n-fold by the loop circuit, then-its effect will be the equivalent of a transmitter of n(1|n) fold resistance connected in the antenna so far as the plate current of the audion is concerned.

and

The mode of modulation herein disclosed has the advantage that it will reduce the distortion as compared with the introduction of the modulating force in the plate circuit alone. This is because the distortion inherent in the telephone transmitter is somewhat opposite in effect to that inherent in the audion. This is illustrated in Fig. 5, where a represents an assuined arbitrary wave form of impressed electromotive force;

b gives ti e Wave form that may be expected from the output of the audion in this case; and c gives the Wave form for the transmitter output when acted upon by asound Wave of the form a. It Will be seen that b and c, when combined., will have a tendency to neutralize the :distortion due to either one alone.

What is claimed is:

l. A modulating system comprising a three-electrode thermionic vacuum tube with input and output circuits and a common conductor connected to the tube ilament, a resistance amplifying loop interposed in said Levage@ conductor, a telephone transmitter interposed in one side of said loop andY a resistance shunting said transmitter.

y2. A modulating system comprising' a three-electrode thermionic vacuum tube with input and output circuits and a common conductor connected to the tube filament, and a telephone transmitter and a resistance amplifying device connected in said conductor.

In testimony whereof, l have signed my name to this specification this 14th day of November, 1923.

JHN STGNE STONE. 

